The present invention relates to polymeric nanocomposite materials with a functional matrix and a method of producing such materials. In particular, the present invention relates to a method of producing polymer-based nanocomposite material in which a functional component, such as a fluorescent dye, is incorporated into either shell-forming polymer to form core-shell latex particles or into both the core and shell. The present invention also relates to use of these nanocomposite materials having multiple read/write capabilities at differing wavelengths for use a memory storage medium.
Two-dimensional (2D) and three-dimensional (3D) ordered arrays of submicron colloid particles have attracted great interest in materials science. Generally, colloid crystals are employed either as templates for producing ordered 2D or 3D structures, (Holland, B T. Blanford, C F, Stein A. Science 1998, 281, 538; Zahidov, A. A. et al. Science 1998, 282, 897; Wijnhoven, J. E. G., Vos, W. L. Science 1998, 281, 802; Lenzmann, F., Li, K., Kitai, A. H., Stxc3x6ver Chem. Mater. 1994, 6, 156) for example, in the fabrication of photonic bang gap materials or on their own right as chemical sensors (Holtz, J. H., Asher, S. A. Nature 1997, 389, 829) and devices for memory storage (Kumacheva, E.; O. Kalinina; Lilge, L. Adv. Mat. 1999, 11, 231). Recently, a new approach to producing 3D polymer-based nanocomposites has been proposed. This method employs latex particles composed of hard cores and somewhat softer shells (Kalinina, O.; Kumacheva. E. Macromolecules 1999, 32, 4122). FIG. 1 generally demonstrates the stages in fabrication of such a nanocomposite material from core-shell latex particles. Core-shell latex particles, composed of hard cores and somewhat softer shells, are synthesized at step A. The particles are packed in a close packed array, at step B, and annealed at step C at the temperature that is above the glass transition temperature, Tg, of the shell-forming polymer (SFP) and below the Tg of the core-forming polymer (CFP). As a result, the latex shells flow and form a matrix, whereas the rigid cores form a disperse phase.
With this approach, it is known to incorporate functional components having different functionalities into the CFP. When the diffusion of the functional component between the cores and the shells is sufficiently suppressed, nanocomposite materials with a periodic modulation in composition are produced. It is also known to prepare materials with a direct structure in which fluorescent core particles are embedded into an optically Inert matrix. U.S. Pat. No. 5,952,131 to Kumacheva et al., the contents of which are incorporated herein by reference, discloses a material having a matrix composed of particles having a core resin and a shell resin. The core resin includes a covalently bonded photosensitive compound that can be selectively excited by light. Diffusion of the fluorescent dye from the cores to the shells was suppressed by covalently bonding the dye to the CFP and crosslinking the CFP at stage A, as shown in FIG. 1 of ""131. The shell resin, when melted at a temperature less than the glass transition temperature of the core resin, forms a continuous phase matrix around the core resin. This material can be used to provide a two- or three-dimensional optical storage medium.
These prior art nanocomposite materials exhibit promising characteristics, especially as memory storage devices. However, by providing functional components in the shell forming polymer matrix, other uses for such nanocomposites, such as photosensitive film coatings, can be developed. While the material described in U.S. Pat. No. 5.952,131 has vastly greater storage capacities than conventional optical storage media, it is desirable to provide increased storage densities, and to increase the data retrieval rate from such media.
It is an object of the present invention to provide nanocomposite materials with a reverse structure such that a functional component, for example, a fluorescent dye, is incorporated into the shell-forming polymer matrix.
In a first embodiment, there is provided a nanocomposite material having a plurality of core particles formed of a core material. The core material has a first glass transition temperature. A shell encapsulates each core particle. The shell is formed of a shell material that has a second glass transition temperature less than the first glass transition temperature. When subjected to a temperature greater than the second glass transition temperature and less than the first glass transition temperature, the shells form a continuous matrix surrounding the core particles. The shell material includes a functional component that can be activated in response to an external excitation. This functional component may be either photosensitive, electro-active, magnetic, piezoelectric, or semiconductor components (it may be a functional polymer or an inert polymer containing chemically or physically incorporated functional species).
It is also an object of the present invention to provide a nanocomposite material that obviates or mitigates at least one disadvantage of the prior art. In particular, it is an object of the present invention to provide a nanocomposite material having an increased storage density, and to provide methods for reading and writing data to such material.
In a first embodiment, there is provided a nanocomposite material having a plurality of core particles formed of a core material that has a first glass transition temperature. A shell encapsulates each of the core particles. The shell is formed of a shell material that has a second glass transition temperature less than the first glass transition temperature. When subjected to a temperature greater than the second glass transition temperature but less than the first glass transition temperature, the shell material forms a continuous matrix surrounding the core particles. Either the shell material or the core material includes a first and a second functional component. The first functional component can be activated in response to a first source of external excitation, while the second functional component can be activated in response to a second source of external excitation. In a preferred embodiment, the first and second functional components are photosensitive dyes that are activated at different wavelengths, supplied by laser sources of different wavelengths. The material of the present invention is particularly suitable for use as a storage medium having multiple bits of data written and read at the same position in the material.
In a further aspect of the present invention, there is provided a method of recording information in the nanocomposite material. The method comprises the steps of selectively activating the first functional component with a first excitation source to addressably write first data, and selectively activating the second functional component with a second excitation source to addressably write second data. The information recorded in the core material using the first excitation source can be read using either the same first source or using another (third) source at a second wavelength if excitation with the first source brings the core material into another stable state. For example, the information can be recorded in the core material can by energizing a core particle with the first excitation source and detecting the information, appearing as a black mark, recorded at that wavelength on the core particle. For the shell materials, the information recorded with second source can be read either with the same source or by using the fourth source with the wavelength different than that of the second source. In a preferred, embodiment, the sources are orthogonally incident on the core particle, and can be energized concurrently.